MR Imaging and Ultrasound of Metatarsalgia—The Lesser Metatarsals

High-resolution Ultrasound of the Foot and Ankle

High-resolution ultrasound (US) can be used to assess soft tissue abnormalities in the foot and ankle. Compared to MRI, it has lower cost, is widely available, allows portability and dynamic assessment. US is an excellent method to evaluate foot and ankle tendon injuries, ligament tears, plantar fascia, peripheral nerves, and the different causes of metatarsalgia.

MR Imaging–Ultrasonography Correlation of Acute and Chronic Foot and Ankle Conditions

Foot and ankle injuries are common musculoskeletal disorders. In the acute setting, ligamentous injuries are most common, whereas fractures, osseous avulsion injuries, tendon and retinaculum tears, and osteochondral injuries are less common. The most common chronic and overuse injuries include osteochondral and articular cartilage defects, tendinopathies, stress fractures, impingement syndromes, and neuropathies. Common forefoot conditions include traumatic and stress fractures, metatarsophalangeal and plantar plate injuries and degenerations, intermittent bursitis, and perineural fibrosis. Ultrasonography is well-suited for evaluating superficial tendons, ligaments, and muscles. MR imaging is best for deeper-located soft tissue structures, articular cartilage, and cancellous bone.

Presurgical Perspective and Postsurgical Evaluation of Plantar Plate and Turf Toe

Capsuloligamentous injury of the first metatarsophalangeal (MTP) joint (eponymously called "turf toe") mostly occurs in athletes and involves acute trauma, whereas tears of the lesser MTP joint plantar plate typically are an attritional-degenerative condition. This article reviews the anatomy, pathophysiology, mechanism and patterns of injury, grading and classification of injury, imaging appearances (pre- and postoperative), and management of first MTP joint capsuloligamentous injuries and lesser MTP joint plantar plate tears. These two distinct pathologies are discussed in separate sections.

Ultrasound findings of plantar plate tears of the lesser metatarsophalangeal joints

Lesser metatarsophalangeal (MTP) joint plantar plate tears are a common and increasingly recognised cause of metatarsalgia, MTP joint instability and forefoot deformity. Increased interest in early accurate diagnosis of plantar plate tears follows recent surgical innovations allowing direct plantar plate repair. The purpose of this review is to describe the ultrasound features of normal lesser MTP joint plantar plates and to characterise and illustrate the direct and indirect ultrasound findings of plantar plate tears. Lesser MTP joint plantar plate tears are most commonly located at the 2nd MTP joint, involving the lateral distal plantar plate insertion with variable propagation medially and proximally. The most common ultrasound appearance of a plantar plate tear is a discrete partial or full thickness hypoechoic defect in the plate substance. Flattening and attenuation or non-visualisation of the plantar plate represent more extensive tears. Dynamic imaging with toe dorsiflexion improves visualisation of tears and augments MTP joint subluxation. A common indirect finding is pericapsular fibrosis along the MTP joint capsule adjacent to a plantar plate tear, which requires differentiation from Morton's neuroma, and key distinguishing features at ultrasound are described. Other indirect findings include the cartilage interface sign, flexor tendon subluxation onto the metatarsal head or medial to the midline, flexor tenosynovitis, proximal phalangeal enthesophytes or avulsion and MTP joint synovitis. Ultrasound offers several advantages over MR imaging but requires a meticulous ultrasound examination, and optimisation of scanning technique is described.

Tips, quips and pearls: Ultrasound-guided distal metatarsal minimal invasive osteotomy (US-DMMO)

Metatarsalgia is a frequent cause of forefoot pain. Surgical treatment is based on the performance of osteotomies at the level of the minor radii to restore a normal distribution of pressure within the forefoot and improve the biomechanics during gait. In recent years, percutaneous surgery of the foot, and specifically distal metatarsal minimal invasive osteotomy, have proven to be a valid technique, providing satisfactory clinical results, similar to open osteotomy with less soft tissue aggression, but it requires intraoperative fluoroscopy to be performed. This article will present a modification to guide the procedure by ultrasound providing a new option that eliminates radiation and provides greater portability and accessibility.

ACR Appropriateness Criteria® Chronic Foot Pain

Chronic foot pain is a frequent clinical complaint, which can significantly impact the quality of live in some individuals. These guidelines define best practices with regards to requisition of imaging studies based on specific clinical scenarios, which have been grouped into different variants. Each variant is accompanied by a brief description of the usefulness, advantages, and limitations of different imaging modalities. The present narrative is the result of an exhaustive assessment of the available literature and a thorough review process by a panel of experts on Musculoskeletal Imaging. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

Lesser Metatarsophalangeal Instability: Diagnosis and Conservative Management of a Common Cause of Metatarsalgia

CONTEXT

Lesser metatarsophalangeal (MTP) instability is a common condition that can become debilitating and require surgery.

EVIDENCE ACQUISITION

An extensive literature review was performed through MEDLINE and Google Scholar for publications relating to the etiology, diagnosis, and treatment of lesser MTP instability using the keywords metatarsophalangeal instability, athlete, forefoot pain, and metatarsalgia from database inception to 2019.

STUDY DESIGN

Clinical review.

LEVEL OF EVIDENCE

Level 4.

RESULTS

Lesser MTP instability is a common condition, especially in the active and aging populations. It is frequently misdiagnosed, causing delays in treatment that allow for progressive pain and deformity, which prevents an active lifestyle. Fortunately, MTP instability can be diagnosed easily with the drawer test. Magnetic resonance imaging is helpful when still in doubt. Conservative treatment entails joint immobilization and gradual return to play with taping and offloading metatarsal pads.

CONCLUSION

Lesser MTP instability is a common diagnosis. Its early detection and conservative treatment can help the patient regain their previous level of activity and avoid surgery.

Utility of power Doppler ultrasonography for detecting forefoot bursae in early rheumatoid arthritis: A case report

RATIONALE

Power Doppler ultrasonography (PDUS) in musculoskeletal ultrasound (MSUS) is a sensitive and reliable method for the assessment of rheumatoid arthritis (RA). The association between ultrasound-detectable forefoot bursae and the development of RA has gained attention. However, a few studies have evaluated the utility of PDUS for examining forefoot bursae in early RA. We report the case of an RA patient who developed reduced foot mobility and had detectable intermetatarsal bursitis with remarkable power Doppler (PD) signals in MSUS at the onset of RA.

PATIENT CONCERNS

A 40-year-old Japanese woman diagnosed with palindromic rheumatism visited our department due to sustained forefoot pain and difficulty walking. The levels of both rheumatoid factor (RF) and anticitrullinated protein antibody (ACPA) were high. She had opening toes with swelling in metatarsophalangeal (MTP) joints. PDUS showed intermetatarsal bursitis with mild MTP synovitis.

DIAGNOSES

We diagnosed RA by comprehensive judgment based on the 2010 American College of Rheumatology and European League Against Rheumatism classification criteria for RA.

INTERVENTIONS

We administered 6.0 mg/wk of methotrexate (MTX) and 2.0 mg/d of prednisolone (PSL) followed by an increase of MTX to 10 mg/wk.

OUTCOMES

After those treatments, the patient's symptoms showed improvement. As of this writing, the patient's remission has been maintained for >2 months.

LESSONS

Her case suggests that PDUS is useful for the detection of forefoot bursitis, and the detection of forefoot bursitis by PDUS may provide the opportunity to make an early diagnosis of RA.

Magnetic resonance imaging of the pulleys of the flexor tendons of the toes at 11.7 T

OBJECTIVE

We obtained high-resolution 11.7-T MR images of the pulleys of the flexor tendons in cadaveric toe specimens. A detailed understanding of toe pulley anatomy as seen with MR is likely to be of benefit in recognizing disease and the effects of trauma.

MATERIAL AND METHODS

Six cadaveric toes were imaged with an 11.7-T small-bore MR imaging system using optimized coils. Two-dimensional dual-echo SE scans were obtained in three planes (40 × 40 × 400-μm(3) voxel size, TE = 7/14 ms, TR = 3,500 ms, fat saturation). Three-dimensional spoiled gradient echo scans were obtained (90-150 μm(3) isotropic voxel size, TE = 6 ms, TR = 25 ms, with and without fat saturation). Specimen orientation was with the long axis of the toe either parallel or perpendicular to B0.

RESULTS

All the annular (A) pulleys were demonstrated in the great and lesser toes. The A2 pulley in the great and lesser toes and the A4 pulley in the lesser toes were the most substantial pulleys. The A5 pulley, which has not previously been described in the toes, was demonstrated. The cruciform pulleys were also seen and were smaller and thinner. Three tissue layers were seen, and there was evidence of different fiber directions in annular pulleys producing different magic angle effects.

CONCLUSION

Detailed anatomy of the pulley system of the flexor tendons was seen on the 11.7-T MR images showing new features and providing a basis for image interpretation. Similarities and differences between the pulley systems in the toes and the fingers were identified.

Static Versus Dynamic Musculoskeletal Ultrasound for Detection of Plantar Plate Pathology

Musculoskeletal ultrasound (US) is a common modality used to examine plantar plate pathology. Comparison of the diagnostic accuracy of static versus dynamic ultrasound has not been previously published. The objective of this study was to prospectively compare the value of using preoperative static and dynamic ultrasound findings to diagnose plantar plate pathology using intraoperative inspection as the standard of reference. Patients attending a single foot and ankle specialty clinic from August 2012 to June 2013 with clinically suspected plantar plate pathology that was unresponsive to conservative care served as the study population. Static and dynamic ultrasound exams were performed by a single experienced rater and compared to intraoperative findings. The overall accuracy, sensitivity, specificity, positive predictive value and negative predictive value were determined for static and dynamic ultrasound exams. Thirty-six patients (45 lesser metatarsophalangeal joints) were included in this analysis. Of the 36 patients, 29 were females and 7 were males with average age of 57.9 ± 7.8 years (range, 38-73). There were 38 plantar plate tears (84.4%) noted on intraoperative examination. The accuracy, sensitivity, specificity, positive predictive value, and negative predictive value for the static US exam were 80.0%, 81.6%, 71.4%, 93.9%, and 41.7%, respectively. The same values for the dynamic US exam were 88.9%, 100%, 28.6%, 88.3%, and 100%, respectively. Static and dynamic ultrasound techniques are each highly sensitive methods for assessing plantar plate pathology. However, the sensitivity and accuracy of the exam is best when dynamic assessment of the plantar plate is employed. Caution should be used when relying solely on static images to diagnose subtle injuries in this area of the foot.

LEVELS OF EVIDENCE

Diagnostic Level II, Prospective.

The reliability of a novel magnetic resonance imaging-based tool for the evaluation of forefoot bursae in patients with rheumatoid arthritis: the FFB score

OBJECTIVE

The aim of this study was to determine the reliability of an MRI-based score that evaluates forefoot bursae (FFBs) in patients with RA.

METHODS

Items for inclusion, grading criteria and MRI sequences were determined iteratively. The score was evaluated in 30 patients with established RA. Reader agreement was evaluated using the percentage of exact/close agreement, Bland-Altman plots, kappa and intraclass correlation coefficient analyses.

RESULTS

The FFB score assesses nine forefoot regions and contains four items: presence, shape, enhancement and magnetic resonance characteristics. The FFB score showed moderate to good intra- and interreader agreement (κ range = 0.5-0.9 and 0.47-0.87, respectively).

CONCLUSION

The FFB score is adequately reliable in the evaluation of bursa-like lesions of the forefoot in patients with RA.

Practical US of the forefoot

Disorders affecting the forefoot are common in the clinical practice. Accurate history and physical examination are the mainstays of diagnosis but imaging modalities are frequently obtained to confirm the clinical suspicion and plan appropriate treatment. In this article we will present the ultrasound (US) technique of examination of the forefoot followed by a brief description of the normal US anatomy and of US appearance of the most frequent forefoot disorders; rheumatoid arthritis, osteoarthritis, overuse arthropathy, Morton neuromas, bursitis, mucoid cysts, foreign bodies, bone disorders.

Forefoot: a basic integrated imaging perspective for radiologists

Imaging of the forefoot is increasingly requested for patients with metatarsalgia. Awareness with specific anatomic arrangements exclusive for the forefoot and widely variable pathologic entities associated with metatarsalgia helps the radiologist to tailor a cost-effective imaging approach. This will enable reaching a specific diagnosis as much as possible with subsequent proper patient management. This pictorial review aims to provide basic understanding for the different imaging modalities used in studying the forefoot. After that, certain anatomic arrangements exclusive for the forefoot are discussed. The final section of this review describes the imaging findings of some common forefoot problems.

Effects of shoe sole hardness on plantar pressure and comfort in older people with forefoot pain

Plantar forefoot pain is common in older people and is related to increased peak pressures under the foot during gait. Variations in the hardness of the shoe sole may therefore influence both the magnitude of loading under the foot and the perceived comfort of the shoe in this population. The aim of this investigation was to determine the effect of varying shoe sole hardness on plantar pressures and comfort in older people with forefoot pain. In-shoe plantar pressures under the forefoot, midfoot and rearfoot were recorded from 35 older people (mean age 73.2, SD 4.5 years) with current or previous forefoot pain using the pedar-X(®) system. Participants walked at their normal comfortable speed along an 8m walkway in shoes with three different levels of sole hardness: soft (Shore A25), medium (Shore A40) and hard (Shore A58). Shoe comfort was measured on a 100mm visual analogue scale. There were statistically significant differences in peak pressure of between 5% and 23% across the forefoot, midfoot and rearfoot (p<0.01). The hard-soled shoe registered the highest peak pressures and the soft-soled shoe the lowest peak pressures. However, no differences in comfort scores across the three shoe conditions were observed. These findings demonstrate that as shoe sole hardness increases, plantar pressure increases, however this does not appear to have a significant effect on shoe comfort.

Musculoskeletal ultrasound for preoperative imaging of the plantar plate: a prospective analysis

The purpose of this study was to prospectively compare preoperative findings on musculoskeletal ultrasound evaluation to observed intraoperative findings for patients undergoing surgical correction of plantar plate tears. Fifty consecutive patients with forefoot pain and a suspected unilateral plantar plate tear at the second metatarsophalangeal (MTP) joint were identified. The same examiner performed a 2-plane (longitudinal and transverse) musculoskeletal ultrasound on the painful second MTP joint. The contralateral second MTP joint was used for comparison. Longitudinal ultrasound images were graded as "torn" or "intact." Transverse ultrasound images were used to localize the suspected pathology. Results of the ultrasound were compared with observed intraoperative pathology. Forty-five plantar plate tears were identified intraoperatively. Longitudinal ultrasound images correctly identified 40 plantar plate tears. The longitudinal ultrasound had a sensitivity of 91.1%, a specificity of 25%, a positive predictive value of 91.1%, and a negative predictive value of 25%. Transverse ultrasound images identified 36 plantar plate tears correctly localizing only 19 tears. Musculoskeletal ultrasound has been widely used to identify and localize pathology in many soft tissue structures. Whereas the longitudinal ultrasound images were useful in identifying plantar plate tears, the same cannot be said about the ability to localize the tear on the transverse ultrasound images. Therefore, ultrasound may not be as good an imaging modality as magnetic resonance imaging for identification and localization of plantar plate pathology.

Plantar pressures and relative lesser metatarsal lengths in older people with and without forefoot pain

Forefoot pain is a common problem in older people. We determined whether plantar pressures during gait and the relative lengths of the lesser metatarsals differ between older people with and without plantar forefoot pain. Dynamic plantar pressure assessment during walking was undertaken using the Tekscan MatScan® system in 118 community-dwelling older people (44 males and 74 females), mean age 74 (standard deviation=5.9) years, 43 (36%) of whom reported current or previous plantar forefoot pain. The relative lengths of metatarsals 1-5 were determined from weightbearing X-rays. Participants with current or previous plantar forefoot pain exhibited significantly (p=0.032) greater peak plantar pressure under metatarsal heads 3-5 (1.93 ± 0.41 kg/cm(2) vs. 1.74 ± 0.48 kg/cm(2) ). However, no differences were found in relative metatarsal lengths between the groups. These findings indicate that older people with forefoot pain generate higher peak plantar pressures under the lateral metatarsal heads when walking, but do not exhibit relatively longer lesser metatarsals. Other factors may be responsible for the observed pressure increase, such as reduced range of motion of the metatarsophalangeal joints and increased stiffness of plantar soft tissues.

Magnetic resonance imaging versus musculoskeletal ultrasound for identification and localization of plantar plate tears

PURPOSE

Plantar plate injuries have been identified as a cause of forefoot pain and deformity. Magnetic resonance imaging (MRI) and musculoskeletal ultrasound (US) have been suggested as appropriate imaging modalities for this pathology. A comparison of these two modalities utilizing intra-operatively pathology as the reference standard has not been published.

METHODOLOGY

51 feet of 42 consecutive patients presenting to clinic with forefoot pain and a suspected unilateral plantar plate tear at the 2nd metatarsophalangeal (MTP) joint were identified. A two plane (longitudinal and transverse) US was performed on the painful second MTP joint. Longitudinal ultrasound images were graded as 'torn' or 'intact'. Transverse ultrasound images were used to localize pathology. All ultrasound exams were performed by the same reconstructive foot & ankle fellow. A pre-operative MRI was performed on these patients and read by a Fellowship Trained Musculoskeletal Radiologist. The physicians reading US and the MRI were blinded to each other's findings.

RESULTS

All 51 feet were examined intra-operatively. 46 plantar plate tears were identified. The sensitivity, specificity, positive predictive value and negative value of MRI were 73.9%, 100%, 100%, 29.4% respectively while the same values for US were 91.5%, 25%, 91.5%, 25% respectively. MRI identified 4 collateral ligaments tears not identified on ultrasound. Discussion &

CONCLUSIONS

Both MRI and US are appropriate modalities for imaging of the plantar plate. While US is a highly sensitive exam, MRI is a more specific exam. Overall these results do not suggest that MR should be replaced by US in all cases.

LEVEL OF EVIDENCE

Diagnostic, Level I.

Ultrasound guided alcohol ablation of Morton's neuroma

BACKGROUND

Morton's neuroma is a common cause of metatarsalgia. This study evaluated the efficacy of ultrasound guided alcohol injection as a treatment for this condition.

METHOD

Data from 87 treatment courses were included in this study with a mean follow of 14.3 months.

RESULTS

Technical success was 100%. One patient developed symptoms consistent with an allergic reaction to the injection and one patient declined further injection because of periprocedural pain. Partial or total treatment response was achieved in 66%, with 32% of patients having complete resolution of pain. The median visual analogue score (VAS) decreased from 8 pre-procedure to 4 post-procedure (p < 0.0001). Procedural success was greater in patients under 55 years old and in those with solitary neuromas. Seventeen patients (20%) went on to have surgery due to continuing pain.

CONCLUSION

Ultrasound guided alcohol ablation for the treatment of Morton's neuroma was a safe procedure that significantly reduced pain and may offer an alternative therapy to surgery.

Assessment of the natural history of forefoot bursae using ultrasonography in patients with rheumatoid arthritis: a twelve-month investigation

OBJECTIVE

To determine the natural history and clinical significance of forefoot bursae over a 12-month period in patients with rheumatoid arthritis (RA).

METHODS

Patients with RA (n=149) attending rheumatology outpatient clinics were assessed at baseline. A total of 120 participants, mean±SD age 60.7±12.1 years and mean±SD disease duration 12.99±10.4 years, completed the 12-month followup (98 women, 22 men, 93 rheumatoid factor positive, 24 rheumatoid factor negative, and 3 unknown). Musculoskeletal ultrasound (US) was used to identify forefoot bursae in all of the participants. Clinical markers of disease activity (well-being visual analog scale [VAS], erythrocyte sedimentation rate [ESR], C-reactive protein [CRP] level, and Disease Activity Score in 28 joints [DAS28]) and foot symptoms on the Leeds Foot Impact Scale (LFIS) Questionnaire were recorded on both occasions.

RESULTS

Presence of US-detectable forefoot bursae was identified in 93.3% of returnee (n=120) participants (individual mean 3.7, range 0-11) at baseline. Significant associations were identified between bursae presence and patient-reported foot impact for impairment/footwear (LFISIF ; baseline: r=0.226, P=0.013 and 12 months: r=0.236, P=0.009) and activity limitation/participation restriction (LFISAP; baseline: r=0.254, P=0.005 and 12 months: r=0.235, P=0.010). After 12 months, 42.5% of participants had an increase in the number of US-detectable forefoot bursae and 45% of participants had a decrease. Changes in bursae number significantly correlated with changes in LFISIF (r=0.216, P=0.018) and LFISAP (r=0.193, P=0.036). No significant associations were identified between changes in bursae and changes in global well-being VAS, ESR, CRP level, or DAS28.

CONCLUSION

The findings of this study suggest that forefoot bursae may regress or hypertrophy over time in patients with RA, and that these changes may be associated with self-reported foot impairment and activity restriction.

Improvement in symptoms and signs in the forefoot of patients with rheumatoid arthritis treated with anti-TNF therapy

Background

Inhibition of tumour necrosis factor (TNF) is an effective way of reducing synovitis and preventing joint damage in rheumatoid arthritis (RA), yet very little is known about its specific effect on foot pain and disability. The aim of this study was to evaluate whether anti-TNF therapy alters the presence of forefoot pathology and/or reduces foot pain and disability.

Methods

Consecutive RA patients starting anti-TNF therapy (infliximab, etanercept, adalimumab) were assessed for presence of synovial hypertrophy and synovitis in the 2^nd and 5^th metatarso-phalangeal (MTP) joints and plantar forefoot bursal hypertrophy before and 12 weeks after therapy. Tender MTP joints and swollen bursae were established clinically by an experienced podiatrist and ultrasound (US) images were acquired and interpreted by a radiologist. Assessment of patient reported disease impact on the foot was performed using the Manchester Foot Pain and Disability Index (MFPDI).

Results

31 patients (24 female, 7 male) with RA (12 seronegative, 19 seropositive) completed the study: mean age 59.6 (SD 10.1) years, disease duration 11.1 (SD 10.5) years, and previous number of Disease Modifying Anti Rheumatic Drugs 3.0 (1.6). Significant differences after therapy were found for Erythrocyte Sedimentation Rate (t = 4.014, p < 0.001), C-reactive protein (t = 3.889, p = 0.001), 28 joint Disease Activity Score (t = 3.712, p = 0.0001), Visual Analog Scale (t = 2.735, p = 0.011) and Manchester Foot Pain and Disability Index (t = 3.712, p = 0.001).

Presence of MTP joint synovial hypertrophy on US was noted in 67.5% of joints at baseline and 54.8% of joints at twelve weeks. Presence of plantar forefoot bursal hypertrophy on US was noted in 83.3% of feet at baseline and 75% at twelve weeks. Although there was a trend for reduction in observed presence of person specific forefoot pathology, when the frequencies were analysed (McNemar) this was not significant.

Conclusions

Significant improvements were seen in patient reported foot pain and disability 12 weeks after commencing TNF inhibition in RA, but this may not be enough time to detect changes in forefoot pathology.

MR arthrography of the second and third metatarsophalangeal joints for the detection of tears of the plantar plate and joint capsule

OBJECTIVE

Tears of the plantar plate and joint capsule of the metatarsophalangeal joint are underrecognized causes of lesser metatarsalgia. This study evaluated MR arthrography for evaluation of this condition in 45 metatarsophalangeal joints in 41 patients.

CONCLUSION

Most metatarsophalangeal joint capsular tears occur at the distal lateral border of the plantar plate, often with injury of the adjacent interosseous tendon. Plantar plate tears are less common. MR arthrography of the metatarsophalangeal joint delineates capsular tears and associated abnormalities.